1. Field of the Invention
The present invention relates to recording sheets for recording information using ink, or the like. In particular, the present invention relates to recording sheets for use with inkjet printers.
2. Description of the Related Art
Commonly used recording sheets for inkjet printing have a three-layered structure as shown in FIG. 3a; an inkjet recording sheet 110 includes a resin film base sheet 111, an ink-receiving layer 112 formed on the base sheet 111, and an ink permeable layer 113 formed on the ink-receiving layer 112.
As shown in FIG. 3b, when an ink drop 114 injected from a nozzle of an inkjet printer (not shown) strikes the surface of the ink permeable layer 113 of the recording sheet 110, a coloring agent and/or a solvent present in the ink permeate through the ink permeable layer 113 and the coloring agent is fixed within the ink-receiving layer 112. The ink fixed within the ink-receiving layer 112 is denoted by reference numeral 117 in FIG. 3b. 
In general, aqueous ink is used for inkjet printers. The conventional recording sheet 110, therefore, uses a hydrophobic resin, such as a water-insoluble polyester resin, which has a low affinity with water, in the water permeable layer 113 in order to allow the aqueous ink to permeate through the layer.
However, aqueous ink typically contains various organic solvents for the purpose of preventing drying ink in addition to water. Examples of such organic solvents include polyols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, polyethylene glycol, and glycerol; alkyl ether derivatives of polyols such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol methyl ethyl ether, triethylene glycol monomethyl ether; ester derivatives of polyols such as ethylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate, glyceryl monoacetate, and glyceryl diacetate; water-soluble amines such as monoethanolamine, diethanolamine, triethanolamine, and polyoxyethylene amine; and nitrogen-containing cyclic compounds such as 2-pyrrolidone, and N-methyl-2-pyrrolidone.
A drawback of these organic solvents is that the high affinity of these solvents to hydrophobic resins such as water-insoluble polyester may cause the ink to disperse laterally in the ink permeable layer, resulting in bleeds in printed images. What is needed, therefore, is a recording sheet that reduces bleeding in printed images.
The present invention provides a recording sheet having an ink-receiving layer and an ink permeable layer, the ink permeable layer being arranged on a surface of the ink-receiving layer and the ink permeable layer is including a filler and a binder, wherein the binder contains as a primary component a water-insoluble polyester resin having a high hydroxyl value in the range of 25 to 65. In one embodiment of the present invention, the filler may contain silica as a primary component.
In one embodiment of the present invention, the recording sheet comprising a base sheet attached to the ink-receiving layer.
In one embodiment of the present invention, the ink-receiving layer comprises at least one resin selected from the group consisting of; natural resins including albumin, casein, starch, gum arabic, and sodium alginate, synthetic resins including carboxymethyl cellulose, hydroxyethyl cellulose, polyamide, polyethylene imine, polyvinyl pyrrolidone, polyvinyl alcohol, polyvinyl acetal, melamin, polyester, polyacryl, polyurethane, and polyallyl amine.
In one embodiment of the preset invention, the filler comprises at least one compound selected from the group consisting of talc, kaolin, clay, zinc oxide, tin oxide, aluminum oxide, aluminum hydroxide, calcium carbonate, titanium white, barium sulfate, titanium dioxide, aluminum silicate, magnesium silicate, magnesium oxide, smectite, zeolite, and diatomite.
In one embodiment of the present invention, the hydroxyl value is in the range between 25 and 45.
In one embodiment of the present invention, the hydroxyl value is in the range between 45 and 60.
In one embodiment of the present invention, the base sheet comprises polyethylene terephthelate.
In one embodiment of the present invention, the base sheet comprises at least one compound selected from the group consisting of polyethylene naphthalate, polyolefins including polyethylene and polypropylene, polyvinyl chloride, polystyrene, polymethyl methacrylate, polycarbonate, transparent paper, cellulose acetate, polyacrylate, and polyether sulfone.